Heredity is the passing on of characteristics from one generation to the next. It is the reason why offspring look like their parents. It also explains why cats always give birth to kittens and never puppies. The process of heredity occurs among all living things including animals, plants, bacteria, protists and fungi. The study of heredity is called genetics and scientists that study heredity are called geneticists.
Through heredity, living things inherit traits from their parents. Traits are physical characteristics. You resemble your parents because you inherited your hair and skin color, nose shape, height, and other traits from them.
Cells are the basic unit of structure and function of all living things. Tiny biochemical structures inside each cell called genes carry traits from one generation to the next. Genes are made of a chemical called DNA (deoxyribonucleic acid). Genes are strung together to form long chains of DNA in structures known as chromosomes. Genes are like blueprints for building a house, except that they carry the plans for building cells, tissues, organs, and bodies. They have the instructions for making the thousands of chemical building blocks in the body. These building blocks are called proteins. Proteins are made of smaller units called amino acids. Differences in genes cause the building of different amino acids and proteins. These differences cause individuals to have different traits such as hair color or blood types.
A gene gives only the potential for the development of a trait. How this potential is achieved depends partly on the interaction of the gene with other genes. But it also depends partly on the environment. For example, a person may have a genetic tendency toward being overweight. But the person's actual weight will depend on such environmental factors as how what kinds of food the person eats and how much exercise that person does.